Treatment with fillers is known since 1980s. Today's most preferred fillers can be classified as hyaluronic acid-based fillers (Hylaform®, Hylaform® Plus, Restylane®, Perlane®, Juvederm®, Juvederm® Ultra, Juvederm® Ultra Plus, Puragen®, Puragen® Plus, Matridur®), collagen based fillers (Zyderm® I, Zyderm® II, Zyplast®, Atelocollagen®, CosmoDerm® I, CosmoDerm® II, Resoplast®) and alginate based fillers (e.g. Novabel®) as described in DE 10 2004 019 241.
Collagen is a natural protein of connective tissue. However, some people suffer from allergic reactions to collagen and thus, an allergy test is always suggested by the practitioner prior to injection of fillers comprising collagen. Hyaluronic acid is a polysaccharide and is naturally found in many tissues of the body. The unfavorable effect of fillers comprising hyaluronic acid is the short-lasting result and the need for multiple injections for an observable effect. Thereby swellings can occur, which decay in 1-3 days. Thus, treatments with collagen and hyaluronic acid based fillers are costly and painful due to the prerequisite of multiple injections and allergy tests. Further reported complications for the fillers is poor syringeability due to high viscosity, aggregation of the particles in the packaging and non-homogeneous distribution of the particles at the injection site.
The use of alginate as filler is known from DE 10 2004 019 241. However, DE 10 2004 019 241 suggests for the long-lasting effect of the cross-linked alginate particles the use of barium (paragraph [0031]).
Therefore, there remains a continuous need for an improved dermal filler with an improved safety profile, an improved tolerability profile, improved application characteristics, and a long-lasting effect.
Chitosan and its derivatives are very well known natural substances and have been employed in the formulation of controlled release systems, i.e. microcapsules and similar colloidal delivery systems. This is documented in several publications, e.g. M. Prabaharan “Review Paper: Chitosan derivatives as promising materials for controlled drug delivery” Journal of Biomaterials Applications, 2008; 23; 5 and in O. Gaserod et al. “Microcapsules of alginate-chitosan—I A quantitative study of the interaction between alginate and chitosan” Biomaterials 19 (1998), 1815-1825; and in Cai et al. “Biodegradable chitosan scaffolds containing microspheres as carriers for controlled transforming growth factor-β1 delivery for cartilage tissue engineering” Chinese Medical Journal 2007; 120 (3); 197-203.
Several methods and reagents have been tested for their ability to crosslink chitosan and to form microspheres. Reaction of chitosan with alginate under different conditions resulted in the formation of microcapsules that had an alginate-chitosan complex membrane including either an alginate or a chitosan core, depending on the reaction conditions (Gaserod et al., loc. cit.). Chitosan microspheres were prepared from chitosan and sodium tripolyphosphate solution (Cai et al., loc. cit.).
WO 2008/103594 describes the use of chitosan and its derivatives as biomaterial for the treatment, repair and/or enhancement of bodily tissue insufficiencies of the vocal chords, muscles, ligaments and cartilage. According to the invention the use of the biomaterial produces a filling effect. Also disclosed are chitosan or chitosan-derivative gels, which optionally include chitin microspheres. In a first step of the chitin microsphere preparation, chitosan microspheres were obtained by spray-drying a chitosan solution in acetic acid/ethanol.
Several publications describe the use of citrate for the cross-linking of chitosan. However, when citrate was added to an emulsion of chitosan in acetic acid-containing solution, only irregular microparticles were formed, and microspheres could only be obtained when gelatin was added and co-emulsified (Shu, X. Z and Zhu, K. J., “Chitosan/gelatin microspheres prepared by modified emulsification and ionotropic gelation”, J. Microencapsulation 2001; 18; 237). Alternatively, microspheres were obtained by dropping a solution containing chitosan and gelatin into a cold oil in order to obtain coagulation of gelatin, prior to cross-linking with citrate (Shu, X. Z and Zhu, K. J., “Controlled drug release properties of ionically cross-linked chitosan beads: the influence of anion structure”, Int. J. Pharm. 2002; 233; 217). Thus, in these publications the term “chitosan microspheres” denotes microspheres comprising cross-linked chitosan and gelatin.